Christopher Reeve says he will walk again – but he’s “just not sure when it’s going to happen.”

“I still think I will [walk],” Reeve tells Barbara Walters on tonight’s “20/20,” in which, for the first time, he shows how he’s able to breathe on his own – via an experimental pacemaker that stimulates his diaphragm.

“A spinal chord injury affects every system in the body – bladder, bowels, sexual function, everything,” says Reeve, paralyzed in a 1995 horse-jumping accident. “So, the more and more that you can get some systems back . . . like the ability to breathe as normal . . . just makes you feel that you’re moving forward.”

Walters then asks Reeve what he’d say to people who say they “don’t want to get out of bed” and face the day.

“Get over it,” the gritty actor responds. “I don’t allow it . . . I get pretty impatient when people are able-bodied but are somehow paralyzed for other reasons . . . and so my recommendation is don’t break your neck to find out that you need to fulfill your potential.”

The interview airs tonight at 10 on Ch. 7.

Last, but not least:

* You want how much? Actress Lena Olin, who played Sydney’s (Jennifer Garner) mom on “Alias,” declined to return for another season – despite producers meeting her $100,000-per-episode demands, according to TV Guide.